Production of bimodal cispolybutadiene



June 15, 1965 D. D. NoRwcoD ETAL. 3,189,592

PRODUCTION 0F BIMODA I CIS--POLYBUTADIENE Filedl Aug. 2s, 1962 NTUINIII United States Patent O 3,189,592 PRODUCTON OF BllVIODAL CIS- POLYBUTADIENE Donald D. Norwood and Leo J. Dagley, Jr., Bartlesville,

Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Aug. 23, 1962, Ser. No. 218,981 5 Claims. (Cl. '260-94.3)

This invention relates to a polymerization process for the production of polymodal cis-polybutadiene.

Among the various new polymers developed from the solution polymerization of conjugated dienes using organometal initiator systems are the high cis polymers of butadiene, polymers formed by 85 to 100 percent cis 1,4- addition. The physical properties of these polymers are such as to make them particularly suitable for heavy duty tires and other articles for which natural rubber has heretofore been preferred.

In the manufacture and processing of these polymers and particularly in their packaging, shipping, and storage, certain diculties have been encountered from their tendency to cold-ow in the unvulcanized state. For example, in the event of cracks or punctures in a package, polymer ilows therefrom, leading to product loss or contamination, sticking together of packages, and the like.

One solution to the problemof cold ow has been the production of cis-polybutadiene having ltwo (bimodal) or more (polymodal) modes or humps in the molecular weight distribution curve. One portion of the polymer should have an inherent Viscosity in the range of approximately 6 to 20 with a iinal polymer in the range of approximately 2 to 5. Preferred products contain 2 to 45 percent by weight of the high inherent viscosity polymer.

VA11 object of this'invention is to provide a new polymerization process which produces cis-polybutadiene with reduced tendency to cold-flow. A further object is to provide a continuous process for the production of polymodal cis-polybutadiene. Other objects and advantages will be apparent to one skilled in lthe art upon reading v this disclosure.

Accompanying and forming a part of this disclosure is a drawing comprising a single figure showing a system for the practice of this invention.

Polymodal cis-polybutadienes have been produced by various methods. One of the better methods is that forming the subject matter of the copending application assigned to the assignee of Ithe present application. This is Naylor, Serial No. 153,354, led November 20, 1961.

Briefly, the process of that application is a 2-step processV in which the catalyst is added sequentially, a high molecular weight polymer being formed in the rst step of the polymerization and a lower molecular weight polymer being formed in the second step. The present process is an improvement thereon. With the initiator systems used for the polymerization of butadiene to produce a polymer having high cis structure, the reaction rate is high during the initial phases of the operation. During this time of high reaction rate minute changes in feed composition or reaction conditions produce a large change in the amount of polymer formed and/or the properties thereof. As the polymerization continues, reaction rate levels off. At about 50 percent conversion, the polymerization becomes considerably slower.

In the present invention, a 2-stage ,polymerization system is used which is continuous and which takes advantage of the reduction in polymerization rate as the reaction proceeds. In the rst stage, the monomer, solvent, and .initiator are added, the initiator being used at a level at which a high molecular weight (high inherent rice viscosity) polymer is produced. The effluent from this rst reaction zone is mixed with additional monomer, solvent, and initiator and further reacted in a second polymerization zone. By the addition of more initiator, the total initiator level in the second polymerization zone is maintained at a level at which the low molecular weight (low inherent viscosity) portion of the polymodal product is produced. Polymerization in both stages is regulated by selection of the amounts of the various ingredients at a point such that roughly 50 percent or higher conversion is obtained in each reactor.

More specifically, our invention provides a continuous two-stage polymerization process for the production of polybutadiene ,in the presence of an initiator obtained by mixing at least one organometal compound as a irst component and a second component containing titanium and iodine, comprising continuously introducing 1,3-butadiene, a hydrocarbon diluent, and initiator to a irst Y polymerization zone, the amount of titanium charged to said rst zone being in the range of 0.02 to 0.15 gram millimols per 100 grams of butadiene, polymerizing 50 to 80 percent of the butadiene charged in said first polym- 'erization zone, continuously withdrawing a first polymerization effluent from said first polymer-ization zone, continuously adding additional butadiene, toluene, and initiator to said first eluent, continuously introducing the resulting mixture into a second polymerization zone, the amount of additional initiator being suiicient to provide an amount of titanium in said second polymerization zone of 0.2 to 2 gram millimols per 100 grams of butadiene charged thereto including that charged to said first zone, and continuing polymerization to an overall conversion of 60 to 90 percent, the amount of butadiene being fed to each of said zones being adjusted so that the iinal polymer product contains 2 to 45 percent by weight of material produced in said rst zone. This process results in lthe production of the high inherent viscosity polymer in the iirst zone and the low inherent Viscosity polymer in the second zone. A particularly useful group of polymer products comprise those in which the final polymer productcontains 12 to 40 percent by weight of material produced in said rst zone.

The specific steps of the invention can be clearly understood from examination of the drawing to which attention is now directed. The essential components of the system include a preform mixer 10, a Step 1 reactor 11 in which high molecular weight polymer is prepared, a second mixer 12, and a Step 2 reactor 13, in which the low molecular weight portion of the final product is produced. Toluene and butadiene are supplied to mixer 1e by conduit 14. Added to this line is a small amount of triisobutylaluminum which functions as a scavenger through line 16. The amount of scavenger to be added must be determined by experiment, the amount varying with the purity of the solvent and monomer being used. Triisobutylaluminum is supplied by conduit 17 and iodine is supplied by conduit 18, these with the titanium tetrachloride charged directly to mixer 10, by means `of conduit 19, functioning as the polymerization initiator. This mixer 10 is provided to insure thorough mixing of the ingredients but no reaction takes place therein because it is relatively small, thereby giving a short residence time. The eiiuent mixture is passed to reactor 11 by means of conduit 21. The effluent from reactor 11 passes to mixer 12 by means of conduit 22, additional toluene, butadiene, triisobutylaluminum, and iodine being supplied to conduit 22 by means of conduits 23, 24, 25 and 26 respectively. Titanium tetrachloride is added by conduit 27. Mixer 12 is provided to insure good mixing of al1 of the components. Good mixing at this point is particularly important because the stream contains the ping the diluent from the polymer.

The polymerization reaction can be carried out under autogenous pressure or at any suitable pressure suicient to maintain the reaction mixture substantially in the liquid phase. The pressure will thus depend upon the particular diluent employed and the temperature at which the plymerization is conducted. However, higher pressures can be employed if desired, these pressures being obtained by some such suitable method as the pressurization of the reactor with a gas which is inert with respect to the polymerization reaction. i

Various materials are known to be detrimental to the catalyst employed in preparing the cis-polybutadiene. These materials include carbon dioxide, oxygen and water. It is usually desirable, therefore, that the butadiene and the diluent be freed of these materials as well as other materials which may tend to inactivate the catalyst. Furthermore, it is desirable to remove air and moisture from the reaction vessel in which the polymerization is to be conducted. Upon completion of the polymerization reaction, the reaction mixture is then treated to inactivate the catalyst and recover the rubbery polymer. A suitable method for accomplishing this result involves steam strip- In another suitable method, a catalyst inactivating material, such as an alcohol, added to the mixture so as to inactivate the catalyst and cause precipitation of the polymer. The polymer is then separated from the alcohol and diluent by any suitable means, such as decantation or liltration. It has been found to be advantageous to add an antioxidant, such as phenyl-beta-naphthylamine, 2,2methylenebis(4 methyl--tertiary-butylphenol), etc., to the polymer solution prior to recovery of the polymer.

The following examples illustrate operation according to our invention but they should not be considered unduly limiting.

In the examples the cold iiow was determined by extruding the rubber through a 1i-inch orifice having a length of 0.107 inch at 3.5 p.s.i. pressure at a temperature of 122 F. After allowing 10 minutes to reach steady state, the rate of extrusion is measured and the value reported in milligrams per minute.

EXAMPLE I The system shown inthe drawing has been used for the production of polymodal cis-polybutadiene. In this operation, reactor 11 (Step 1) was operated at 70 F. and reactor 13 (Step 2) at 40 F. Residence time in the mixer was approximately 28 seconds; in reactor 11, 2.5 hours; in mixer 12, 6.4 minutes, and in reactor 13, 1.5 hours. Conversion was 50 percent in the Step 1 reactor with an overall conversion of 70 percent. Over 85 percent of the polymer was formed by cis 1,4-addition and the product had a cold ow of approximately 2. The material balance for this operation is shown in the following table:

run the product was formed by greater than 85 percent 1,4-addition.

RUN 1 [Recipe, parts by weight] Step 1 Overall* Butadiene 100 100 1,200 Triisobutylaluminum 0. 60 (3. 04 mhm) Iodine 0. 0399 0. 224 (0 158 mhm) (0.88 mhm) Titanium tetrachloride 0. 0171 0. 096 (0 09 mhm) 0 s1 mhm) Scavenger (triisobutylaluminum) Y 0. 14

RUN 2 Overall Step 1 Run 2A Run 2B (first 30 hrs.) (next 17 hrs.)

i 100 100 V100 Y. Toluene- 1,800 1, 500 1, 700 Triisobutylaluminulm 0. 0298 0. 730 0. 700 (0.15 mhm) (3 68 mhm) (3. 54 mhm) Iodine 0. 0382 0. 272 0. 261 (0 15 mhm) (1 07 mhm) (1.03 mhm) Titanium tetrachloride 0. 0142 0. 117 0. 112 (0.075 mhm) (0. 62 mhm) (0.59 mhm) Scavenger (triisobutylaluminum) 0. 18

Run 1 Run 2A Run 2B Total time of run, hours 3s au 17 Residence time, hours 6. 1 6. 2 6. 5 3. 2 2. 5 3. (l 40 High molecular weight portion of product, wt. percent 38 29 35 Mooney of product (ML-4 at 212 F.).- 30 22 22 Cold flow 1. 56 2. 53 2. 53

*Ratio present in-Step 2 reactor.

For the inherent viscosity determination, one tenth gram of polymer was placed in a wire cagemade from 80 mesh screen and the cage was placed in 100 m1. of Ytoluene contained in a wide-mouth, 4ounce bottle. After the polymer remained in contact with the solvent for 24 5o hours at room temperature (approximately 25 C.), the

brated with toluene. The relative viscosity is the ratio High Low Conduit Toluene Butadiene Triisobutyl- Iodine Titanium molecular molecular aluminum tetrachloride weight welght rubber rubber EXAMPLE II of the viscosity of the polymer solution to that of toluene.

Additional runs have also been made and details of some of these are set forth in the following table, the recipes first being given followed by the details of the polymerization and analysis of the products.

In each The inherent viscosity is calculated by dividing the natural logarithm of the relative viscosity by the Weight of the original sample.

To determine the amount of the molecular structure of the various types, the polymers can be dissolved incarbon "disulde'to form a-solution having 25 grams of polymer per liter of solution.` The infrared spectrum of such a solution (percent transmission) is then determined in a Vcommercial infrared spectrometer.`

The-percent ofthe total unsaturation present as trans f 1,4- is calculated according to the following equation and consistent units: Y Y

4where: e=extnction coeicient Y`(liters-molsLcentimeters-1); E=extinction (log 10/1 t=path length (centimeters); and Vc=concentration `(rnols double bond/liter).

' The extinction is determined at'the 10.35 micron'rband Vrand, the extinction Vco'eicient used is 146 (liters-mols-l- Y centimetersrl). Y Y

The percentof the total unsaturation present as-1,2 (or "yinyl) is calculated according to the above equation, using `the l11.0 'micron'band and an extinction Vcoeiticient of V209 liters-mols-lgcentimeters1 The'percent of the total unsaturation present as cis 1,4-

Y is obtained'by subtracting the trans 1,4- 'and1,2` (vinyl) Y determinedaccordingto. the above methods from the theo- Aretical unsaturation assuming one double bond per each C4 unit in the polymer.

Operation according tothe present invention" is particularly satisfactory because it is a simple matter to'control conditions in each ofthe reaction zzones. Operation at higher polymerization temperatures somewhat reduces the ciscontent of the final polymer. Thiszmust be balanced against thedesire to obtain good conversion rates by Yusing more Aelevated temperatures. YThe 70 and 40 F.V temperatures setforthrinxample VI provide a good compromise in this matter.

Another variable which iseasy to control Yis the monomer to solvent ratio Vpresent in each-reactor. In'the reac-V tor in which the high .molecular weight polymer is produced, the viscosity Vcan reach a limitingfactor which Y Y interferes with eiective heattransfer. When the viscosity inthe reactor goes much above 3000 centipoises, heat 'transfer becomes difficult, although Vwe. have worked'with 'viscosities' as high as approvimately V4000 centipoises.

Therefore, as shownrbythe'examples, wefprefer to operate with a higher solvent to monomerV ratio inthe first Y -step of theprocessV and alowerfsolvent-tomonomer'ratio in the second step.; `Viscosity control is less'diicult where the lower molecular weightpolymer` is concerned Y and, thisisrtheV polymer whichis presentto the greatest extent'in the efuentfrom the low Vmolecular Weight Vre-actori .Y J Y VThe productsproduced according toxour'invention are useful in making Ytires vand otherrubbe'r articles.

usual compounding recipesin preparing vulcanized products are Vused'includingV softeners, filters, and Vcuratures- It `is sometimes ydesirable to blend the .polymodal cis-Y polybutadiene with SBR,` natural rubber, and the like.

As many possible embodiments can'ben'iade of this invention without departing from the scope thereof, it is to be understood thatall matter herein set forth is to be interpreted as illustrative and not as unduly limiting the invention.V

We claim:

1. A continuous two-stage .polymerization process for the production of polybutadiene containing atleast 85 per- -The cent.V cis-l,4,addition in ,the presence of an initiator obtained by mixing at least Yone organometal compoundr'as a first component and a second iodine containing componentrcontaininga titanium'hali'de, comprising continu- Y- ously Vintroducing Y and initiator to a iirst polymerization zone, the amount ofY 1,3-butadiene, a hydrocarbon diluent,

' titanium charged to'said Vrst zone being 'inthe range vpolymerization zone, continuously adding additional'butaof 0.02v to 0.15 gram millimols per 100 Vgrams of butadiene, Vpolyinerizing 50 to 8O percent ofthe butadiene charged` in said first polymerization zone, continuously withdrawing a rstpolymerization eiiluent from said first( diene, toluene, and Vinitiatorto said irst eiiuent, `continu- Y ously'introducingthe resulting mixtureinto a second polymerization zone, the amount of additional initiatorbeing sufficient to provide an amount of titaniumin said second polymerization zone ofO;2to 2 gram millimolsperrv100 Vbutadiene being fed toeach of said zonesv being .adjusted soV grams of butadiene charged thereto includingthatcharged 1 to fsaidriirst zone, and continuing polymerization-to anV overallzconversionof 60 to `90 percent, thetamou'nt'of f'that the iinalpolymer product YcontainsZ Vto .45 percent byweight of material produced in said first zone.

V2.-"The Vprocess of claim 1 wherein Vsaid rst .zone Vis operated at ahigher temperature thanrsaid second.

f3. :The process of claim 1 wherein the ratio of butadieneV .to toluene is higher in'said second zone than in said first.

4. The process of claim Y1 .wherein the final polymerV product lcontains -l2't 40 percent Vby Weight of; material producedin saidrst-zone.

YA5. lA continuous two-stagepolymerization processV for Y the iproduction of polybutadiene containingatlleastjS.

percent cis-1,4-additionin the presence of 1a triisobutyl-V 1 aluminum-iodine-titanium Vtetrachloride. initiator fsystem;

the mol ratio .of titaniumk tetrachloride toriodine being-.inV

'the range of 10:1 to 0.72521`and saidftriisobutylaluminum Y. being gpre'sentin anzamount of ll to;20 Yrnol's per mol ofY titaniumftetrachloride, icomprising continuously introduc- Y ,ing 1,-3butadiene, toluene, and initiator to a firstfpolymerizationg'zone, the' amount'- of 'Y titanium tetrachloride charged to said first zone being in therange of 0L02-to 0.15 gram millimols peralOO-'grams of 'butadienepolym.

erizing 50 to'80 percent. of theibutadiene charged inrsaid first polymerization zone, continuously withdrawing a 'rst polymerization effluent from said first polymerization zone, continuously adding additional.butadieneytoluenmV .andinitiator to said rst erfliuent, continuously introducing :the:resultingrnixtureinto Va second polymerization zone,

the amount .of additional initiatorV being suicientto profV videan amount of titanium tetrachloride insaid'second 1 zonel ofv0.2to Zgrammillimol-s per 100 gramsof butadiene charged thereto including that chargedlto saidffirst zone, and*continuing,polymerization'toan overall conversion ofA 60 to 90 percent, the amount of Vbutadiene beingV Yfedtoeach of saidzonesbeingf adjusted so that the VfinalV polymer product contains 2 to `45 percent '.by weightv of material produced insaid rst zone. Y 5 j References Cited by the Examiner n V UNITED sTATEs PATENTS 2,999,102.39` 9*/61 :short et a1. r e -r 26a-$4.3

3,057,840 10/{62Y Pouock r -.-26o-94.3

JOSEPH L. SCHOFER, Primary Examiner. 

1. A CONTINUOUS TWO-STAGE POLYMERIZATION PROCESS FOR THE PRODUCTION OF POLYBUTADIENE CONTAINING AT LEAST 85 PERCENT CIS-1,4,-ADDITION IN THE PRESENCE OF AN INITIATOR OBTAINED BY MIXING AT LEAST ONE ORGANOMETAL COMPOUND AS A FIRST COMPONENT AND A SECOND IODIEN CONTAINING COMPONENT CONTAINING A TITANIUM HALIDE, COMPRISING CONTINUOUSLY INTRODUCING 1,3-BUTADIENE, A HYDROCARBON DILUENT, AND INITIATOR TO A FIRST POLYMERIZATION ZONE, THE AMOUNT OF TITANIUM CHARGED TO SAID FIRST ZONE BEING IN THE RANGE OF 0.02 TO 0.15 GRAM MILLIMOLS PER 100 GRAMS OF BUTADIENE, POLYMERIZING 50 TO 80 PERCENT OF THE BUTADIENE CHARGED IN SAID FIRST POLYMERIZATION ZONE, CONTINUOUSLY WITHDRAWING A FIRST POLYMERIZATION EFFLUENT FROM SAID FIRST POLYMERIZATION ZONE, CONTINUOUSLY ADDING ADDITIONAL BUTADIENE, TOLUENE, AND INITIATOR TO SAID FIRST EFFLUENT, CONTINUOUSLY INTRODUCING THE RESULTING MIXTURE INTO A SECOND POLYMERIZATION ZONE, THE AMOUNT AF ADDITIONAL INITIATOR BEING SUFFICIENT TO PROVIDE AN AMOUNT OF TITANIUM IN SAID SECOND POLYMERIZATION ZONE OF 0.2 TO 2 GRAM MILLIMOLS PER 100 GRAMS OF BUTADIENE CHARGED THERETO INCLUDING THAT CHARGED TO SAID FIRST ZONE, AND CONTINUING POLYMERIZATION TO AN OVERALL CONVERSION OF 60 TO 90 PERCENT, THE AMOUNT OF BUTADIENE BEING FED TO EACH OF SAID ZONES BEING ADJUSTED SO THAT THE FINAL POLYMER PRODUCT CONTAINS 2 TO 45 PERCENT BY WEIGHT OF MATERIAL PRODUCED IN SAID FIRST ZONE. 